The Calera Creek Water Recycling Plant will answer for a history of serious sewage overflows with a $1.7 million fine and a total overhaul of its sewer maintenance system under a settlement reached with the San Francisco Bay Regional Water Quality Control Board.

The penalty was imposed after a water board investigation in 2009 revealed that millions of gallons of sewage-tainted stormwater escaped into the ocean in a series of preventable sanitary sewer overflows. During one storm in 2008, approximately 7 million gallons of raw sewage, mixed with rainwater, were discharged from the wastewater plant into the ocean after the plant became overwhelmed.

Pacifica spent millions of dollars to build a new, state-of-the-art sewage-treatment plant in 2000, a move that was prompted by a cease-and-desist order imposed by the water quality board for sewage violations throughout the 1990s.

The latest fine was reduced from $2.3 million when the city agreed to a 10-year infrastructure improvement plan with strict benchmarks. It will cost millions of dollars to comply, and those funds will almost certainly come from increased sewer fees, according to wastewater officials.

“We are bringing on four new people, because they’re requiring that we clean our sewer system, and we TV our system every working day,” said Dave Gromm, director of the plant. “TV” means putting a camera into pipes to spot holes and other problems.

The wastewater plant overhaul was important, but it didn’t come close to solving the problem, said Lila Tang, chief of the wastewater control program at the water board.

“They did a good job upgrading the treatment plant, but after that they sort of sat back and waited for the next catastrophe,” she said.

There won’t be many more catastrophes if the sewage treatment plant adheres to a multipart plan that would eliminate sanitary sewer overflows due to rainfall by 2020.

Those actions include a systemwide cleaning program of all sewer mains; an inventory of all problems, especially leaks caused by intrusion from tree roots; a new computerized record-keeping program; and the development of a long-term capital improvement plan that will pay for the repair and replacement of the most serious pipeline failures.

The water board will vote on whether to formally approve the proposed settlement agreement at a hearing May 11.

But Gromm said the city is already moving forward with the first two requirements, a sanitary sewer overflow reduction plan and a master plan based on a systemwide evaluation.

Tang said the evaluation is overdue.

The cornerstone of the settlement will involve a new ordinance requiring Pacifica residents with leaky sewer laterals to pay to replace them.

Sewer laterals are the private sewer lines that connect homes to the city’s trunk lines.

Gromm blames leaky sewer laterals for most of the stormwater overflows. He said they absorb groundwater when it rains and inundate the sewage treatment plant.

“We can see the trunk sewers are in very good shape, but the laterals are just pouring clear water. Every home is like that in certain areas,” Gromm said.

Unlike other cities on the Peninsula, these sewer lateral repairs would not be voluntary. Repairing or replacing a sewer lateral can cost up to $4,500 per household, according to Gromm.

The good news is that the water board will permit the city to apply $600,000 of its fine toward a special fund that helps homeowners replace sewer laterals when needed — what Tang calls “sugarcoating on the bitter pill.”

How the city will pay for all the capital-improvement needs that will emerge in the next year is another question. Gromm said the city can afford to put $1 million into a special account for infrastructure improvements.

He said the money would have to come from raising sewer fees for ratepayers.

Sewer fees go up every year in Pacifica.

“We can only pay for what we can pay for,” Gromm said. “We’re not going to be able to do everything in one year.”